Spine stiffening device

TECHNICAL FIELD

p-0002This invention relates generally to therapeutic and corrective devices and methods for the spine and more specifically relates to devices and methods for stiffening the spine.

BACKGROUND

p-0003The spine includes a series of joints routinely called motion segment units, which is the smallest component of the spine that exhibits kinematic behavior characteristic of the entire spine. The motion segment unit is capable of flexion, extension, lateral bending and translation. The components of each motion segment unit include two adjacent vertebrae and their apophyseal joints, the intervertebral disc, and the connecting ligamentous tissue. Each component of the motion segment unit contributes to the mechanical stability of the joint.

p-0004Components of a motion segment that move out of position or become damaged can lead to serious pain and may lead to further injury to other components of the spine. Depending upon the severity of the structural changes that occur, treatment may include fusion, discectomy, or laminectomy.

p-0005Underlying causes of structural changes in the motion segment unit leading to instability include trauma, degeneration, aging, disease, surgery, and the like. The purpose of fusion or rigid stabilization is the immobilization of a motion segment unit. Thus, fusion or rigid stabilization of one or more motion segment units may be an important element of a surgical procedure in certain cases (i.e., injuries, deformities, tumors, etc.). In other cases it is a complementary element (i.e., fusion performed due to degeneration).

p-0006One current spinal surgical technique typically involves fusing one or more unstable motion segment units and possibly, the removal of ligaments, bone, disc, or combinations thereof included in the unstable motion segment unit or units prior to fusing. However, fusion often involves several disadvantages. For example, the fusing process results in a permanent or rigid internal fixation of all or part of the intervertebral joints and usually involves metallic rods, plates, and the like for stabilization. Such systems are intended to rigidly immobilize the motion segment unit to promote fusion within that motion segment unit resulting in a loss of mobility.

p-0007Fusion also causes the mobility of the motion segment to be transferred to other motion segments of the spine. The added stresses transferred to motion segments neighboring or nearby the fused segment can cause or accelerate degeneration of those segments. Another disadvantage of fusion is that it is an irreversible procedure.

p-0008Spinal fixation systems using orthopedic rods as described above provide a relatively rigid construct. Another type of spinal treatment technique offers dynamic stabilization for the spine. One example of a dynamic stabilization system is provided by the assignee of this invention under the trademark DYNESYS® as generally described in European Patent Application No. 0669109A1 which is hereby incorporated by reference in its entirety. Such a dynamic stabilization system utilizes pedicle screws installed into appropriate locations in adjacent vertebrae. Flexible materials in conjunction with the pedicle screws are used rather than rigid orthopedic rods or bone grafts alone as an adjunct fusion. A tubular spacer is positioned between the pedicle screws on adjacent vertebrae with a tensioned cord passing through the central lumen of the spacer. Dynamic stabilization systems of this type bring the lumbar vertebrae into a desired anatomical position while stabilizing the effective segments and without irreversible fusion.

p-0009Fusion procedures can be improved by modifying the load sharing characteristics of the treated spine and one technique is to allow more of a physiologic loading between pedicular fixation and anterior column support. Additionally, a device and associated method that precludes or at least delays the need for fusion for all but the most advanced degeneration of a motion segment, particularly if such a device would allow close to normal motion and pain relief is desirable. Moreover, utilization of minimally invasive surgical procedures and techniques to install such devices is also a highly desirable objective to enhance and promote patient healing and recovery.

SUMMARY OF THE INVENTION

p-0010This invention addresses these and other shortcomings in the prior art. In various embodiments, the invention includes a spinal stabilization system having a first and a second vertebral anchor each adapted to be coupled to one of a first and a second vertebrae. The system also includes a flexible connecting element coupled to each of the first and second vertebral anchors and extending between the vertebral anchors. The connecting element has a central member and a brace positioned about the central member and the central member is stiffer than the brace to provide the needed combination of support and stiffness to the construct while offering flexibility.

p-0011In other embodiments of this invention, the spinal stabilization construct includes first and a second top loading polyaxial pedicle screw each adapted to be coupled to one of a first and a second vertebrae. The construct also includes a flexible connecting element coupled to each of the first and second pedicle screws and extending between the pedicle screws. The connecting element has a central member. A first and a second securing member are each threadably coupled to one of the pedicle screws to secure the connecting element thereto. A brace is positioned concentrically about the central member and the central member is stiffer than the brace. A first and a second shank extend in opposite directions from the central member and each shank is coupled to one of the pedicle screws. A first and a second flange are on the connecting element and the flanges are spaced on opposite sides of the brace.

p-0012The spinal stabilization system may also include a third and a fourth flange on the connecting element, each of which are spaced on opposite sides of the central member, embedded in the brace and spaced from the first and second flanges.

p-0013Other embodiments of a spinal stabilization system according to this invention include a first and a second vertebral anchor each adapted to be coupled to one of a first and a second vertebrae and a flexible connecting element coupled to each of the first and second vertebral anchors and extending between the vertebral anchors. The connecting element has a central member and a brace positioned about the central member. A first and a second flange are each on the connecting element and spaced on opposite sides of the brace. The system may also include a first and a second shank extending in opposite directions from the first and second flanges, respectively. Each shank is coupled to one of the vertebral anchors. A third and a fourth flange may be included on the connecting element and spaced on opposite sides of the central member, embedded in the brace and spaced from the first and second flanges. The first and second flanges may be integrally formed with the first and second shanks, respectively.

p-0014In another embodiment of this invention, the spinal stabilization includes a first and a second polyaxial pedicle screw each adapted to be coupled to one of a first and a second vertebrae. A flexible connecting element is coupled to each of the first and second polyaxial pedicle screws and extends between the pedicle screws. A first and a second securing member are each threadably coupled to one of the pedicle screws to secure the connecting element thereto. The flexible connecting element may be integrally formed from a polymeric, elastomeric or non-metallic material.

p-0015These and other various embodiments of this invention offer an improvement over known systems by providing stabilization of the vertebral column while allowing for flexibility and axial dampening.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

<figref idrefs="DRAWINGS">FIG. 1</figref> is perspective view of a spinal stabilization construct according to a first embodiment of this invention;

<figref idrefs="DRAWINGS">FIG. 2</figref> is a side elevational view of the system of <figref idrefs="DRAWINGS">FIG. 1</figref> being installed on a patient's vertebral column;

<figref idrefs="DRAWINGS">FIG. 3</figref> is a cross-sectional view of a flexible connecting element of the embodiment of <figref idrefs="DRAWINGS">FIG. 1</figref>;

<figref idrefs="DRAWINGS">FIG. 4</figref> is a cross-sectional view of another embodiment of a flexible connecting element according to this invention;

<figref idrefs="DRAWINGS">FIG. 5</figref> is a cross-sectional view of a still further embodiment of a flexible connecting element according to this invention;

<figref idrefs="DRAWINGS">FIG. 6</figref> is a perspective view of a multi-level spinal stabilization system according to another embodiment of this invention;

<figref idrefs="DRAWINGS">FIG. 7</figref> is a perspective view of a still further embodiment of a flexible connecting element for use in a spinal stabilization system according to this invention;

<figref idrefs="DRAWINGS">FIG. 8</figref> is cross-sectional view of the flexible connecting element of <figref idrefs="DRAWINGS">FIG. 7</figref>;

<figref idrefs="DRAWINGS">FIG. 9</figref> is a perspective view of a still further embodiment of a flexible connecting element for use in a spinal stabilization system according to this invention;

<figref idrefs="DRAWINGS">FIG. 10A</figref> is a disassembled, perspective view of the flexible connecting element of <figref idrefs="DRAWINGS">FIG. 9</figref>;

<figref idrefs="DRAWINGS">FIG. 10B</figref> is a partially disassembled view of the spinal stabilization system utilizing the flexible connecting element of <figref idrefs="DRAWINGS">FIGS. 9 and 10A</figref>;

<figref idrefs="DRAWINGS">FIG. 11</figref> is a cross-sectional view of the assembled spinal stabilization system of <figref idrefs="DRAWINGS">FIG. 10B</figref>; and

<figref idrefs="DRAWINGS">FIG. 12</figref> is a view similar to <figref idrefs="DRAWINGS">FIG. 11</figref> of a multi-level spinal stabilization system.

DETAILED DESCRIPTION OF THE INVENTION

p-0030Referring to <figref idrefs="DRAWINGS">FIG. 1</figref>, one embodiment of a spine stiffening stabilization system <b>10</b> is shown and includes a connecting element <b>12</b> coupled to and extending between a pair of vertebral anchors <b>14</b>. Each vertebral anchor <b>14</b> is adapted to couple to either of two vertebras <b>16</b> in a patient's spine <b>18</b>. With the connecting element <b>12</b> secured to the vertebral anchors <b>14</b>, the connecting element <b>12</b> maintains a restored disc space height and/or alignment between the adjacent vertebrae <b>16</b>. In one form, the connecting element <b>12</b> preserves motion between the adjacent vertebrae <b>16</b>.

p-0031In one embodiment as shown in the various drawings, such as <figref idrefs="DRAWINGS">FIGS. 1</figref>, <b>2</b>, <b>10</b>B, and <b>11</b>, the vertebral anchor <b>14</b> is a polyaxial, top loading pedicle screw including a threaded shaft <b>20</b> adapted to be inserted into a pedicle area <b>22</b> of the vertebrae <b>16</b>. The vertebral anchor includes a head <b>24</b> on the threaded shaft <b>20</b> and a saddle <b>26</b> is coupled to the head <b>24</b> and is adapted for polyaxial movement of the saddle <b>26</b> relative to the shaft <b>20</b>. The saddle <b>26</b> having an exemplary U-shape provides a top loading capability to the vertebral anchor <b>14</b> so that the connecting element <b>12</b> may be inserted downwardly into the saddle <b>26</b> between a pair of polyaxial head receiving arms <b>28</b>. The saddle <b>26</b> can be constructed with any desired shape. A securing member in the form of a threaded set screw <b>30</b> mates with the saddle <b>26</b> to secure the connecting element <b>12</b> to the vertebral anchor <b>14</b>. Each receiving arm <b>28</b> of the U-shaped saddle <b>26</b> has threads <b>32</b> which mate with the threads <b>34</b> on the set screw securing member <b>30</b>. While a top loading polyaxial pedicle screw is shown and described herein as one embodiment of the vertebral anchor <b>14</b>, other types of vertebral anchors can readily be used within the scope of this invention including standard fixed pedicle screws, hooks or other devices intended to couple a connecting element to the vertebrae.

p-0032Referring to <figref idrefs="DRAWINGS">FIGS. 1-3</figref>, one embodiment of the connecting element <b>12</b> according to this invention includes a central portion or member <b>36</b> and a pair of connecting portions or shanks <b>38</b> that include rod portions <b>39</b> that can be of any suitable shape to fit within the saddle <b>26</b> extending in opposite directions on the connecting element <b>12</b>. Each shank <b>38</b> is coupled to one of the vertebral anchors <b>14</b>. The terminal ends of the shanks <b>38</b> of the various embodiments of this invention can be trimmed to length after sizing and installation. Alternatively, the connecting members <b>38</b> can be pre-sized prior to implementation. The central member <b>36</b> is concentrically surrounded by a flexible portion or brace <b>40</b>. The brace <b>40</b> is positioned between spaced flanges <b>42</b> and the central member <b>36</b> is secured within the brace <b>40</b> and between the flanges <b>42</b> by crimping tabs <b>44</b>.

p-0033The connecting element <b>12</b> of this invention includes a flexible intermediate portion <b>46</b>. In one embodiment, the brace <b>40</b> and central member <b>36</b> are intended for use in the intermediate portion <b>46</b>. Alternatively, a solid flexible core can be used as the flexible intermediate portion <b>46</b>. In one embodiment, the brace <b>40</b> is an elastomeric member that allows for flexing of the connecting element <b>12</b>. The brace <b>40</b> stabilizes the spine <b>18</b> while allowing for flexibility and axial dampening. In one embodiment, the central member <b>36</b> is tensioned and integral to the intermediate portion <b>46</b> of the connecting element <b>12</b>. The central member <b>36</b> allows for bending of the shanks <b>38</b> and the associated forces on the brace <b>40</b>. Unlike standard spine rods which provide little or no flexibility and axial dampening, the connecting element <b>12</b> of this invention allows for flexing of the spinal stabilization system <b>10</b> in response to movement of the vertebrae <b>16</b>. The configuration and interaction of the various component parts of the connecting element <b>12</b> of <figref idrefs="DRAWINGS">FIGS. 1-3</figref> allows for bending of the connecting element <b>12</b> and the shanks <b>38</b> connected to the vertebral anchors <b>14</b> so that the central member <b>36</b> is placed under tension and one side of the brace <b>40</b> is compressed depending upon the orientation of the bending motion.

p-0034Referring to <figref idrefs="DRAWINGS">FIG. 4</figref>, a cross-sectional view of an alternative embodiment of the connecting element <b>12</b> according to this invention is shown in which the shanks <b>38</b> are connected to a pair of spaced outer flanges <b>42</b> between which the flexible brace <b>40</b> is positioned. The central member <b>36</b> is embedded within the brace <b>40</b> and includes an additional pair of spaced inner flanges <b>48</b> between which a portion of the central member <b>36</b> is held by mechanical crimping tabs <b>44</b> or similar arrangement. Each of the inner flanges <b>48</b> is mounted and spaced from an associated outer flange <b>42</b> by an extension <b>50</b> of the shank <b>38</b> extending into the brace <b>40</b>. The embodiment of <figref idrefs="DRAWINGS">FIG. 4</figref> allows the shanks <b>38</b> and flanges <b>42</b> when bent to apply both compressive and tensile forces to the brace <b>40</b> as well as tension to the central member <b>36</b>. The central member <b>36</b> according to various embodiments of this invention may be made from a Dacron™ tape woven cord, a braided stainless steel or titanium cable, carbon fiber, Kevlar™ or a variety of other materials providing sufficient strength with low elongation characteristics. Other options for the central member <b>36</b> include a synthetic or natural rubber woven cord which is stretched between the flanges <b>42</b> prior to attachment and mounting therein. The cord would be attached to the flanges <b>42</b> and then stretched into a mold cavity where the polymer or elastomer brace material would be injected into the mold so that the central cord would be in constant tension, but below its elastic limit.

p-0035A further alternative embodiment of the connecting element <b>12</b> according to this invention is shown in <figref idrefs="DRAWINGS">FIG. 5</figref> in which the central member <b>36</b> is surrounded by the brace <b>40</b> and oppositely extending shanks <b>38</b> mount the connecting element <b>12</b> to the respective vertebral anchors <b>14</b>. The central member <b>36</b> of <figref idrefs="DRAWINGS">FIG. 5</figref> may be en elastic mesh or woven member and the polymer material of the brace <b>40</b> would then be injection molded through the mesh and around the corded central member. The central member <b>36</b> could be steel, titanium, nickel titanium alloy, polymer, carbon fiber or other materials. In the various embodiments, the connecting element <b>12</b> is a flexible member that provides a shock absorbing effect in transmitting spinal column loads between the anchors <b>14</b> to which it is engaged. Intermediate portion <b>46</b> between the flanges <b>42</b> can also permit relative movement to allow motion of the spinal column segment to which connecting element <b>12</b> is engaged. In one embodiment, intermediate portion <b>46</b> provides connecting element <b>12</b> with a variable stiffness profile between anchors <b>14</b>.

p-0036For installation requiring more than one level of treatment, a two-level section system <b>10</b> such as the embodiment shown in <figref idrefs="DRAWINGS">FIG. 6</figref> could be utilized. The construct of <figref idrefs="DRAWINGS">FIG. 6</figref> provides two flexible connecting elements <b>12</b> with a predetermined space between them. The length of the shank <b>38</b> positioned between the connecting elements <b>12</b> of the embodiment of <figref idrefs="DRAWINGS">FIG. 6</figref> could be fixed or a variable distance to accommodate different vertebral anatomies.

p-0037A further alternative embodiment of a spinal stabilization stiffening system <b>10</b> according to this invention is shown in perspective view in <figref idrefs="DRAWINGS">FIG. 7</figref> and cross-sectional view in <figref idrefs="DRAWINGS">FIG. 8</figref>. The vertebral anchor <b>14</b> of the embodiment of <figref idrefs="DRAWINGS">FIGS. 7 and 8</figref> is shown as a pedicle screw having a threaded shaft <b>20</b> and a head <b>24</b>. The vertebral anchor <b>14</b> in one embodiment is a polyaxial pedicle screw similar to a device marketed by Zimmer Spine, Inc. as the ST360™. The vertebral anchor <b>14</b> includes an upwardly extending toggle <b>62</b>. The connecting element <b>12</b> is mounted to the toggles <b>62</b> of the vertebral anchors <b>14</b>. The connecting element <b>12</b> in one embodiment includes a central member <b>36</b> of an elastomeric or polymeric material providing flexibility to the construct. The central member <b>36</b> is molded about a pair of rims <b>64</b> providing an aperture <b>66</b> so that the connecting element <b>12</b> may be mounted downwardly onto the toggles <b>62</b> and secured in place by a washer <b>68</b> and threaded nut <b>70</b> combination as shown in <figref idrefs="DRAWINGS">FIGS. 7 and 8</figref>.

p-0038Referring to <figref idrefs="DRAWINGS">FIGS. 9-11</figref>, a further alternative embodiment of the connecting element <b>12</b> according to this invention is shown. In this embodiment, flanges <b>38</b> are provided with outwardly projecting annular hubs <b>52</b> and a securing element in the form of a setscrew <b>54</b> is seated within a threaded aperture <b>56</b> on the hub <b>52</b> to secure the flange <b>42</b> and hub <b>52</b> arrangement to the shank <b>38</b> of the connecting element <b>12</b> and against the brace <b>40</b>. The connecting element can be assembled pre- or intra-operatively. Once assembled, as shown in <figref idrefs="DRAWINGS">FIG. 10A</figref>, the connecting element <b>12</b> is positioned in the top loading vertebral anchors <b>14</b> and secured thereto by the vertebral anchor set screws <b>30</b> as shown in <figref idrefs="DRAWINGS">FIG. 10B</figref> resulting in the arrangement and installation of <figref idrefs="DRAWINGS">FIG. 9</figref>. In this embodiment, the intermediate portion <b>46</b> is of a different size than intermediate portion <b>46</b> of <figref idrefs="DRAWINGS">FIG. 1</figref> and occupies more of the distance between the securing members <b>30</b>. A cross-sectional view of the connecting element <b>12</b> and associated vertebral anchors <b>14</b> of <figref idrefs="DRAWINGS">FIGS. 9-10B</figref> is shown in <figref idrefs="DRAWINGS">FIG. 11</figref>.

p-0039In a still further embodiment shown in <figref idrefs="DRAWINGS">FIG. 12</figref>, a multi-level construct <b>10</b> is provided with a generally H-shaped hub <b>58</b> having a duct <b>60</b> there through for the central member <b>36</b> to extend from one connecting element <b>12</b> to an adjacent connecting element <b>12</b>.

p-0040The flanges <b>42</b> can be adapted to engage the flexible brace <b>40</b> there between. In one embodiment, flanges <b>42</b> include holes to receive attachment means such as fasteners, sutures, threads, wires, or other devices to engage central member <b>36</b> to the respective flange <b>42</b>. In another embodiment, the brace <b>40</b> is injection molded between flanges <b>42</b>. The injected material can flow into holes in the central member <b>36</b> to form around central member <b>36</b> and at least partially around the flanges <b>42</b> to provide engagement therewith. In still another embodiment, intermediate portion <b>46</b> is molded over flanges <b>42</b>. In any embodiment, the connecting element <b>12</b> can be provided with or without the central member <b>36</b> and with or without the flanges <b>42</b>.

p-0041In one procedure, anchor <b>14</b> is engageable to a first vertebra <b>16</b>, a second anchor <b>14</b> is engageable to a second vertebra <b>16</b> and a third anchor <b>14</b> is engageable to a third vertebra <b>16</b>. When so engaged, intermediate portion <b>46</b> allows the vertebrae to which the anchors <b>14</b> are engaged to move or flex relative to one another, but limits extension and flexion motion to provide a stabilizing effect.

p-0042Connecting element <b>12</b> can be guided into position between the anchors <b>14</b> using an installation instrument as discussed above. The installation instrument may include extenders extending from any one, two or three of the anchors <b>14</b>. Other techniques contemplate insertion with an open surgical technique, or guiding of the connecting element <b>12</b> distally along extenders extending proximally from one or more of the anchors <b>14</b>. Connecting element <b>12</b> can be employed in fusion procedures or in procedures employing dynamic stabilization without fusion. In fusion procedures, fusion promoting material and/or one or more fusion devices, implants, or bone graft are placed in the disc space between adjacent vertebrae. In such procedures, a single level connecting element <b>12</b> may be coupled between the vertebrae if dynamic stabilization is desired. If rigid stabilization is desired, an elongated connecting element <b>12</b> can be provided and engaged between the vertebrae to be fused, and one or more adjacent vertebral levels can be dynamically stabilized with the intermediate portion <b>46</b> engaged between these or more other vertebral levels.

p-0043While in the illustrated embodiments the connecting elements <b>12</b> are shown as being adapted to extend along one or two vertebral levels, the connecting elements <b>12</b> can also extend along three or more vertebral levels. For example, one of the shanks <b>38</b> can include a length that extends along multiple vertebral levels to be fused to provide rigid stabilization of these levels, while the other of the shanks <b>38</b> includes a length adapted to extend along at least one vertebral level to provide a flexible intermediate portion <b>46</b> between vertebrae <b>16</b> for dynamic stabilization.

p-0044The flexible brace <b>40</b> discussed herein can be made from any suitable material allowing at some motion of the vertebral level along which the intermediate portion <b>46</b> is engaged. For example, the brace portions <b>40</b> can be made from elastomers, polycarbonateurethane, polyetheretherketone, or other polymer material. The brace <b>40</b> can be made from resorbable material. In still another form, the brace <b>40</b> include springs, which can be made from metal or other suitable material.

p-0045It is further contemplated that the connecting element <b>12</b> can be provided with a varying stiffness profiles to vary the stiffness properties of the system <b>10</b> and control movement of the one or more dynamically stabilized vertebral levels. Such varying stiffness profiles can be provided across the cross-section of a single flexible intermediate portion <b>46</b> of a particular connecting element <b>12</b>, or provided between different intermediate portions <b>46</b> of a single multi-level connecting element <b>12</b>, or provided between a number of connecting elements <b>12</b> in a kit where the connecting elements <b>12</b> includes one or more portions with a stiffness profile that varies relative to one or more of the portions of the other connecting elements <b>12</b>.

p-0046In one embodiment, the hardness characteristics of the material comprising the flexible brace <b>40</b> is varied. For example, the durometer of an elastomer material comprising the one or more flexible brace portions <b>40</b> may vary to allow selection and implantation of a connecting element <b>12</b> providing the desired motion characteristics for the vertebral level.

p-0047In another embodiment, the connecting element <b>12</b> is provided with a central member <b>36</b> that couples the first and second flanges <b>42</b> to one another through the flexible brace portion <b>40</b>. The diameter of the central member <b>36</b> can be varied so that the connecting elements <b>12</b> with flexible brace portions <b>40</b> extending about a central member <b>36</b> with a greater diameter are stiffer than connecting elements <b>12</b> with a flexible brace portion <b>40</b> extending about a central member <b>36</b> of lesser diameter.

p-0048In a further embodiment, the central member <b>36</b> can be pre-tensioned so that the flanges <b>42</b> are compressed against the flexible brace portion <b>40</b> when engaged thereto. The amount of pre-tension can range from zero to the tensile break strength of the central member <b>36</b>. The greater pre-tension loading of the central member <b>36</b> results in stiffer flexible brace portion <b>40</b> behavior since the preloading compresses the flexible brace portion <b>40</b> between the flanges <b>42</b>.

p-0049From the above disclosure of the general principles of the invention and the preceding detailed description of at least one embodiment, those skilled in the art will readily comprehend the various modifications to which this invention is susceptible. Therefore, we desire to be limited only by the scope of the following claims and equivalents thereof.